Speedo Gear Calculator

At the bottom of the speedometer face, look for the numbers 940, 960, 1000, or 1020. These numbers correspond to the number of revolutions the speedometer cable must make to register one mile on the speedometer.
Most older GM speedometers are 1000.

Use the Tire Height Calculator at the bottom of the page to figure the tire height if you don't know it.

Speedo Input:

Speedometer Revolutions Per Mile:

Rear Tire Overall Diameter:

Differential Gear Ratio:

Want to find: Gear

Drive or Driven Gear teeth (opposite to selected above)

Click to calculate the gear needed:

Gear needed: teeth

To reset the form input:

Tire Height Calculator

Tire Height & Width Calculator

Tire Width(mm)

Aspect Ratio(1-100)

Wheel Diameter(in)

Tire Height(in)

Tire Width(in)

0.00

0.00

Enter the tire width in millimeters, the aspect ratio,
the wheel diameter in inches, and
Click on Calculate...